wing slats ?

[terence seymour]

G,Day I am looking for information on wing slats i.e. Do they need to be the same profile as the top leading edge of the wing ,and run level with the leading edge, and how far back over the wing do they go, and what is the distance above the wing, and do thy run level to the top of the
wing or do they taper up or down. I would be grateful for any information thanks TERRY.

[Chris Lane]

Hi Terence,

Off-hand, without researching it, I don't know the answers to these points but it is the SLOT you have to form. The SLAT forms the upper boundary and it's inner profile normally matches the wing surface at the slat closed position. The outer profile completes an airfoil section for the slat.

The provision of slots on wings can be for different purposes. Usually they are intended to maintain airflow over the ailerons near the stall in order to resist spin tendency. Accordingly their length is the same as the ailerons. On biplanes it was usual to provide slats only on the upper wings, even if these wings did not have ailerons, to delay tip stall. Alternatively slats can be provided full span in conjunction with slotted trailing edge flaps to create a wing section capable of maintaining the lift at very low airspeeds.

Most of the de Haviland Moths had automatic slats on the upper wings to create the slots when they popped out. They were simply sheet alloy bent to match the upper wing surface and leading edge profile. They deployed when the wing incidence increased to the point where the leading edge stagnation point had moved round the LE below the slat allowing it to lift and deploy. As a typical low-speed wing section stalls at around 16 degrees AOA the leading edge "wrap" of the slat needs to a couple of degrees less than this. Mechanically such slats are part of a "4-bar chain". This allows the slat to lift and move forward to the open position. When the wing incidence reduces the slat simply blows shut. The hinge arm lengths and pivot locations have to be chosen to provide the correct closed and open geometry.

By contrast the Druine Turbulent has fixed, built-in, slots within the existing wing section and these are particularly easy to model.

The Scottish Aviation Pioneer and "Twin-Pin" had fully selectable slats which, with slotted flaps, allowed incredibly short take-off or landing. Accordingly they are full span.

If your project is scale then I recommend simply scaling direct from the prototype. If not then the Roger Druine approach is certainly the most straight forward.

Although this does not answer your questions I hope it may give you some pointers.

Chris

[David Whiteley]

Again, I do not have detailed knowledge or information on this topic, but only an observation.

A friend had a second hand model Feisler Storche (sp?) which had leading edge slats - although they were not moveable. This model was almost unflyable. It was well balanced, and unwarped, but it had a vile need to bank. It was then noticed that one slat was slightly nearer to the wing than the other. With this corrected it flew well.

[Rob Buckley]

Terry, as with a lot of things, it depends!

As we all know, the slat is used to 'boost' the airflow over the top of the wing and delay stall at higher angles of attack, like the picture below.

As you won't have hundreds of hours to spend in a wind tunnel to get the configuration spot on, if you're doing a scale model, copy what the fullsize designers did. If you're doing a non-scale model, find a similar fullsize and copy that.

If the wing is straight, the slats will be constant section & gap. If the wing is tapered, the slats will generally shrink as they go outboard to match the corresponding shrink in aerofoil size.

[ian redshaw]

Hi Terence, I have a bit of experience in things slattery. I've designed them for a Bf109E, Tiger Moth, Storch and the latest on a Handley Page HP42. The HP42 ones are fully automatic. I put servo on them initially as a safety device so I could lock them shut but in reality, from the second flight onwards the servos on them have been just along for the ride. With the servos not now being used, I cannot open or close the slats, they are free to do as they wish independantly of one another. The main thing with the design is the 'gap' must decrease from bottom to top. This is achieved in the geometry actuation arms, or the geometry of whatever method used on the full size. Tiger Moths use a very similar design to the HP42, whereas the Bf109 uses a fully internal method but the same principle applies, smaller gap at the top (back) larger gap at the bottom (front) Here hopefully is a scale sketch of the system on the HP42, plus a link to a fab Tbobborap YouTube vid of them in operation. In the video the slats chatter a bit due to the turbulent air of the day. As it flies through rising air the differences between lifting and airspeed pressures make the slats operate for no apparent reason. On the HP the slats really do work great, keeping the ailerons working even though the model is actually stalled.

Hope this helps, let us see how you get on, any more details to share??

Ian.

https://www.youtube.com/watch?v=GMW2b8JvHA8

[terence seymour]

G,DAY Ian thanks for your reply and all others who replied. I have decided to have fixed slats al/la Storch.
As the wing is built awaiting covering and fixed slats will require less mulering to the wing.
I have made the slats over the w/end and made the fixings but still unsure of the ventry I was thinking one and a half Ins air in down to three quarters Ins out what do you think ?? the wing is 102" long 20"with with quite a large airfoil 24" ailerons 15" flaps all x 5" wide would appreciate your thoughts. The slats are 36" long x three and a half " wide. thanks TERRY.